This invention relates generally to optical instruments and methods, and, more particularly, relates to apparatus and methods for scanning a surface or other object with an optical beam, detecting the light emitted from or transmitted by the object, and generating an image of the object.
Scanning imaging techniques are employed in scanning laser microscopes (SLM), confocal scanning laser microscopes (CSLM), tandem scanning confocal microscopes (TSM), scanning laser ophthalmoscopes (SLO), flying spot television (FSTV) devices, and other applications. Confocal imaging systems can provide enhancements in contrast and in dynamic range. Certain of these imaging systems include moving optical elements for deflecting a laser beam, so that an illumination spot is swept across the object to be scanned. Other such systems employ mechanical elements to rotate an illuminated pinhole for the same purpose. In the TSM, a plurality of illumination spots is moved simultaneously, to provide source multiplexing, necessary because the source does not have the higher radiance (brightness) of a laser.
A double scanning optical apparatus is disclosed in U.S. Pat. No. 4,764,005 of Webb et al. The apparatus utilizes multiple scanning elements, including a multi-faceted rotating polygonal reflector scanner, to provide scanning of both incident and reflected light at television-rate frequencies.
Additionally, certain flying spot imagers use a cathode ray tube (CRT) as a light source, with a single illuminated point scanned across the CRT face. The tube face is imaged onto the object to provide the illumination raster.
A TSM is discussed in Petran et al., "Tandem-Scanning Reflected-Light Microscope," Journal of the Optical Society of America, Vol. 58, No. 5, pp. 661-664, May 1968. Petran et al. acknowledge that reflected-light microscopy of semi-transparent material is usually unsatisfactory because of low contrast and light scattering, and describe the TSM, in which both the object plane and the image plane are scanned in tandem. As a result, only light reflected from the object plane is included in the image. In the Petran et al. system, the object is illuminated with light passing through holes in one sector or side of a rotating scanning disk, known as a Nipkow disc. The scanning disk is imaged by the objective at the object plane. Reflected-light images of these spots are directed to the diametrically opposite side of the same disk. Light can pass from the source to the object plane, and from the object plane to the image plane, only through optically congruent holes on diametrically opposite sides of the rotating disk. This configuration produces an image having enhanced contrast and sharpness relative to a conventional reflected-light microscope.
Tandem scanning confocal arrangements and flying spot CRT configurations, however, are "light-starved" by the limited brightness of the illumination spot. In TSM configurations, this brightness limitation is partially compensated by the multiplex operation. TSM systems, however, are hampered by stray light scattered from the moving pinhole array.
Current flying spot systems benefit from the advent of the laser. A number of scanning laser ophthalmoscopes (SLO), for example, employ a laser beam scanned by moving electromechanical elements. A scanning ophthalmoscope of this type is disclosed in U.S. Pat. No. 4,213,678 of Pomerantzeff et al. The ophthalmoscope discussed therein utilizes a laser source to produce a narrow output beam, and a mechanical device for scanning the beam across the fundus of an eye. A confocal scanning laser ophthalmoscope (CSLO) is disclosed in Webb et al., "Confocal Scanning Laser Ophthalmoscope," Applied Optics, Vol. 26, No. 8, Apr. 15, 1987, pp. 1492-1499. The CSLO scans an illumination spot over the object of interest, and synchronously scans a detector over the image. Other confocal devices, are discussed in The Handbook of Biological Confocal Microscopy, Pawley, ed., IMR Press, 1989.
Conventional scanning laser devices, however, necessitate a multiplicity of mechanical components moving at high speed. They are typically bulky, require significant power to drive the scanning mechanism, and generally provide only a predetermined scanning pattern.
It is accordingly an object of this invention to provide improved scanning-type imaging methods and apparatus.
A further object of the invention is to provide such methods and apparatus affording high spatial resolution, enhanced brightness, increased dynamic range, and a selectable, or random-access, scanning pattern.
It is another object of the invention to provide such imaging methods and apparatus capable of being implemented in a compact and reliable embodiment.
A further object of the invention is to provide display or illumination devices having high brightness.
Other general and specific objects of the invention will in part be obvious and will in part appear hereinafter.